The present invention relates to a method for recording a large number of information at one time to a magnetic recording medium. In particular, the invention relates to a magnetic transfer method for transferring recording information to a magnetic recording medium of large capacity and high recording density.
With rapid propagation and progress in the technique to utilize digital image, the amount of information processed by devices such as personal computer has extensively increased. To cope with the increase of the amount of information, there are now strong demands on a magnetic recording medium, which has large capacity for information recording and is available at low cost, and further, can record and read within shorter time.
In a high-density recording medium, e.g. hard disk or large capacity removable type magnetic recording medium such as ZIP (Iomega Inc.), the information recording region has narrower tracks compared with floppy disk. In order to accurately scan the magnetic head with narrower track width and to record and reproduce signals at high S/N ratio, it is necessary to perform accurate scanning by using tracking servo technique.
In this respect, for a large capacity magnetic recording medium such as hard disk, removable type magnetic recording medium, etc., the so-called xe2x80x9cpreformattingxe2x80x9d is performed, i.e. servo signals for tracking, address information signals, reproduction clock signals, etc. are recorded with a given spacing within one turn of the disk.
The magnetic head reads the preformat signals and corrects its own position, and it can run accurately on the track.
At present, the preformatting is performed as follows: Using a special-purpose servo recording system, disks are recorded one by one and track by track. The servo recording system is very expensive and long time is required for the preformatting, and this gives considerable influence on the manufacturing cost.
For this reason, techniques of magnetic transfer without resorting to the track-by-track preformatting have been proposed. For instance, transfer techniques are proposed in JP-63183623 (A), EP-0915456 JP-10-40544 and JP-10-269566). However, there has been no proposal suitable for practical application so far, e.g. proposals on the condition of magnetic field to be applied at the time of transfer or on the means for generating magnetic field.
As a recording method to solve the above problems, EP-0915456 proposes the following method: Surface irregularities (i.e. convex and concave portions) corresponding to information signals are formed on the surface of a base material. On a master carrier for magnetic transfer, ferromagnetic thin film is formed at least on the surface of convex portions, and this master carrier is brought into contact with the surface of a sheet-type or disk-type magnetic recording medium where ferromagnetic thin film or ferromagnetic powder coating layer is formed. Or, AC bias magnetic field or DC magnetic field is applied, and the ferromagnetic material on the surface of the convex portion is excited. Then, magnetized patterns corresponding to convex and concave portions are recorded on the magnetic recording medium.
According to this method, the surface of the convex portions of the master carrier for magnetic transfer is brought into close contact with the magnetic recording medium to be preformatted, i.e. a slave medium. By exiting the ferromagnetic material on the convex portions, a predetermined format is formed on the slave medium. Thus, static recording can be carried out without changing relative positions of the master carrier and the slave medium, and accurate preformat recording can be achieved. Moreover, the time required for the recording is very short. Specifically, in the method for recording from the magnetic head as described above, the time of several to several tens of minutes is required for recording, and the time required for magnetic transfer is further extended in proportion to the recording capacity. By the new magnetic transfer method, magnetic transfer can be achieved within one second regardless of the recording capacity or recording density.
According to this method for magnetic transfer, the surface of convex portions of the master carrier for magnetic transfer is brought into close contact with the magnetic recording medium to be preformatted, i.e. the slave medium, and the ferromagnetic material of the convex portions is excited. Then, a predetermined preformat information is recorded on the slave medium. By this method, static recording can be achieved without changing relative positions of the master carrier and the slave medium, and accurate preformat recording can be performed. Also, this method is characterized in that the time required for the recording is very short.
However, warping of several xcexcm occurs unavoidably on a substrate used as the slave medium. For this reason, in order to perform magnetic transfer on both surfaces of the slave medium at the same time, it is necessary to bring the master carrier into contact with the slave medium from both surfaces. To maintain close contact with the slave medium, strong force is required for compression.
As a result, when magnetic transfer is repeatedly performed, the master carrier for magnetic transfer may be damaged when it is brought into close contact with the slave medium. In this respect, to improve durability of the master carrier for magnetic transfer, it has been practiced to perform magnetic transfer on one surface at a time.
However, a problem arises when magnetic transfer is performed on one surface at a time. Specifically, when magnetic field is applied on a surface opposite to the surface of the slave medium, on which magnetic transfer has been already performed, the magnetic recording signals already recorded may be erased or may drop off.
To solve the above problems, it is an object of the present invention to provide a stable transfer method, by which the master carrier for magnetic transfer is brought into close contact with one surface of the slave medium at a time. Then, an external magnetic field is applied, and inaccurate servo operation on the slave medium is prevented which occurs as the result of the transfer of the preformat pattern.
The present invention provides a method for performing magnetic transfer by bringing a master carrier for magnetic transfer and a slave medium in close contact with each other and by applying a magnetic field for transfer, whereby a product (Ms1xcex41) of saturation magnetization (Ms1) and film thickness (xcex41) of a magnetic layer of the master carrier to be used for magnetic transfer on a surface of the slave medium with earlier magnetic transfer and a product (Ms2xcex42) of saturation magnetization (Ms2) and film thickness (xcex42) of a magnetic layer of the master carrier to be used for magnetic transfer on the other surface of the slave medium with subsequent magnetic transfer are in a relation of: 1.5 less than (Ms2xcex42)/(Ms1xcex41) less than 10, and a transfer magnetic field (Hdu1) applied to the surface with the earlier magnetic transfer and a transfer magnetic field (Hdu2) on the surface of the slave medium with the subsequent magnetic transfer are in a relation of: 0.2xe2x89xa6Hdu2/Hdu1xe2x89xa60.9.
Further, the present invention provides a magnetic transfer method as described above, wherein magnetic transfer performed using the master carrier for magnetic transfer with a magnetic layer formed on a portion corresponding to an information signal on the surface of a substrate and the slave medium to receive magnetic transfer, the slave medium is first magnetized by initial DC magnetization in track direction (see FIG. 1(a), the master carrier for magnetic transfer is brought into close contact with the slave medium processed by initial DC magnetization, and magnetic transfer is preformed by applying a transfer magnetic field in a direction opposite to the direction of the initial DC magnetization on the surface of the slave medium.
Also, the present invention provides a magnetic recording medium as described above, wherein a product (Ms1 xcex41) of saturation magnetization (Ms1) and film thickness (xcex41) of a magnetic layer of the master carrier for transfer of the servo signal used for magnetic transfer to a surface with earlier magnetic transfer and a product (Ms2 xcex42) of saturation magnetization (Ms2) and film thickness (xcex42) of a magnetic layer of the master carrier for transfer of the servo signal used for transfer to a surface of the magnetic recording medium of the subsequent magnetic transfer are in a relation of: 1.5 less than (Ms2xcex42)/(Ms1xcex41) less than 10, and the servo signal is transferred under the condition that a transfer magnetic field (Hdu1) on the surface with the earlier magnetic transfer and a transfer magnetic field (Hdu2) on the surface of the magnetic recording medium with the subsequent magnetic transfer are in a relation of: 0.2xe2x89xa6Hdu2/Hdu1xe2x89xa60.9.
Further, the present invention provides a magnetic recording medium as described above, wherein the magnetic recording medium is first magnetized by initial DC magnetization in track direction, the master carrier for transferring the servo signal is brought into close contact with the magnetic recording medium processed by the initial DC magnetization, a magnetic field for transfer is applied in a direction opposite to the direction of the initial DC magnetization on the surface of the magnetic recording medium, and the servo signal is transferred by magnetic transfer.
Also, the present invention provides a magnetic recording medium as described above, wherein the magnetic recording medium is a floppy disk type magnetic recording medium comprising a flexible base material or a hard disk type magnetic recording medium comprising a rigid base material.